As a former Marylander, if you decide to travel through the state without having a concealed permit for Maryland (and don't separate the guns and ammo, and store them away from you - ammo/mags in glove box and weapon unloaded in your trunk) you run the risk of getting hauled in if you're caught speeding, etc. God help you if someone notices your weapon at a rest stop or gas station. Do I think it's stupid? Yes. But hey, dem's the breaks.
As far as reciprocity goes, yes, the states that honor your state's permit do just that - honor it. This allows you to carry concealed in those states without the need for that state's particular permit. However, some states have varying laws regarding concealed carry, so you will need to consult
www.handgunlaw.us or similar informative sites (ideally, the state's own statutes) regarding places where carry is not allowed, and various state's definitions of deadly force and when it's applicable. Generally speaking, most states that have "Shall-Issue" laws are typically similar when it comes to their definitions of things like this, but it always pays to be 100% sure.
Do some research, DON'T drive through Maryland concealed/loaded, be safe and have a Merry Christmas!